Workaround QueryInterface not properly mutating services.contentPrefs.

common/modules/sanitizer.jsm

@@ -70,7 +70,6 @@ var Sanitizer = Module("sanitizer", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakRef
 
         util.addObserver(this);
 
-        services.add("contentPrefs", "@mozilla.org/content-pref/service;1", Ci.nsIContentPrefService);
         services.add("cookies",      "@mozilla.org/cookiemanager;1",        [Ci.nsICookieManager, Ci.nsICookieManager2,
                                                                              Ci.nsICookieService]);
         services.add("loginManager", "@mozilla.org/login-manager;1",        Ci.nsILoginManager);

common/modules/services.jsm

@@ -126,7 +126,7 @@ var Services = Module("Services", {
             if (!service.interfaces.length)
                 return res.wrappedJSObject || res;
 
-            service.interfaces.forEach(function (iface) res.QueryInterface(Ci[iface]));
+            service.interfaces.forEach(function (iface) res instanceof Ci[iface]);
             if (service.init && args.length) {
                 if (service.callable)
                     res[service.init].apply(res, args);